1. Field of the Invention
This invention relates generally to laser devices. More particularly, the present invention relates to a laser device of the type which utilizes a semiconductor laser chip enclosed in a package.
2. Description of the Prior Art
A typical semiconductor laser chip used in a laser device has such a structure as shown in FIG. 29 of the accompanying drawings.
Specifically, as shown in FIG. 29, the laser chip designated by reference numeral 3 has a multilayer crystal sandwiched between a pair of electrodes 3d, 3e. The multilayer crystal includes a surface layer formed with a stripe 3b, and an intermediate activation layer 3a formed with a light generating region 3c in corresponding relation to the stripe 3b. When a voltage is applied across the pair of electrodes 3d, 3e, excitation occurs in the light generating region 3c and emits an output laser beam A from its front facet 3f along a longitudinal axis of the laser chip while emitting a monitor laser beam A' from its rear facet 3g.
Such a semiconductor laser chip is known to generate a considerable heat at the time of laser beam emission. Further, the laser chip is also known to be adversely affected by humidity or other external factors. Thus, it is necessary to take some measure for effectively dissipating heat and for protecting the laser chip against adverse external factors.
One way to overcome the above-described problems is to enclose the semiconductor laser chip in a package which also has a function of dissipating heat, as disclosed in U.S. Pat. No. 5,089,861 or U.S. Pat. No. 5,140,384 for example. A more specific structure of the package-type semiconductor laser device is now described with reference to FIGS. 30-32 of the accompanying drawings.
As shown in FIGS. 30-32, the package-type semiconductor laser device comprises a metallic heat sink plate 1 (which is usually referred to as "stem") having a diameter D and a thickness T. The stem 1 is integrally formed with an upright mounting block 2, and a semiconductor laser chip 3 is mounted on the mounting block 2 via a sub-mount 4. The laser chip 3 together with the sub-mount 4 and the mounting block 2 is enclosed in a cap 5 having a window opening closed by a glass plate 6.
The stem 1 is formed with a pair of perforations 1a for receiving a corresponding pair of leads 7 fixed in place by glass sealant 8. Another lead 7 is attached to the underside of the stem 1. Further, the stem 1 is also formed with an inclined recess 1b under the laser chip 3 for mounting a monitoring photodiode 9, and associated components are electrically connected by wires W.
With the arrangement described above, the stem or heat sink plate 1 effectively dissipates heat at the time of laser beam emission, whereas the cap 5 prevents entry of adverse external substances. However, the prior art laser device still has the following problems.
First, since the glass window 6 is located vertically above the stem 1, the laser chip 3 must be oriented vertically to emit an output laser beam A toward the window 6. Such an orientation of the laser chip 3 necessitates the provision of the upright mounting block 2. As a result, the overall height H of the laser device must be at least larger than the sum of the stem thickness T and the block height. Thus, it is difficult to reduce the size of the laser device.
Secondly, since the stem 1 must be made of a metal such as carbon steel (because of its function for heat dissipation), it is rather time-taking to integrally form the upright mounting block 2 by forging. Thus, the production cost of the laser device increases due to the presence of the upright mounting block 2.
In the third place, the process step for sealing the perforations 1a of the stem 1 is rather troublesome because such sealing must be performed with the leads 7 held inserted in the perforations 1a. Thus, this process step results in an additional cost increase.